1. Field of the Invention
The present invention relates to a synchronization circuit for optical disc apparatuses and a synchronization method for optical disc apparatuses.
2. Description of the Related Art
Various recording media and recording/playback apparatuses associated therewith have been developed, and compact disc (CD) systems, mini-disc (MD) systems, DVD (Digital Video Disc/Digital Versatile Disc) systems, and the like are known. A recording/playback apparatus in such disc systems is provided with a defect signal detection circuit (or simply called a defect circuit) so that failures in playback operation and/or the quality of playback sound do not occur due to scratches or stains on a disc. Refer to, for example, Japanese Patent Application Laid-open Publication No. 10 208244. As shown in FIGS. 1 and 7 of the foregoing Publication, the defect signal detection circuit detects physical defects such as scratches or stains on a disc and the drop-out (loss) of recorded data due to, for example, an operation error when recording (hereinafter, generically called “defects”) by using information obtained from the disc by the optical head. A defect signal is output as a signal indicating the detection result, and based on the defect signal, a predetermined defect handling process is performed in, for example, the decoder performing playback signal processing or the servo system circuit. By this means, interruptions to playback voice and failure occurrence in servo operation are prevented.
In performing the above-mentioned defect handling process, the defect signal detection circuit outputs a defect signal that is at, for example, “HIGH” during the time when the playback RF signal is lost (drop-out) due to a defect as shown in FIG. 9 of the above Publication. By this means, a synchronization detection circuit prohibits the detection of frame synchronization signals during the time when the defect signal is output, and resumes the detection of frame synchronization signals when the defect signal ceases to be output.
However, in a conventional synchronization detection circuit, for some time after the defect signal falls from “HIGH”, the playback RF signal has not yet fully recovered and is still in a transient state. If in the transient state of the playback RF signal, the detection of frame synchronization signals is resumed, genuine correct frame synchronization signals cannot be obtained, and thus the desired defect handling process cannot be performed.